The present invention relates to logic-built-in-self-test (LBIST) of macros, and more specifically, to an LBIST diagnostic method for root cause identification.
A macro in an integrated circuit, for example, is an instruction sequence that implements a logic circuit (e.g., AND gate) when executed. LBIST includes hardware elements, software elements, or a combination of the two built into an integrated circuit (IC) to allow self-tests of the macros. The LBIST may use an architecture that is referred to as self-test using MISR and parallel SRSG (STUMPS) architecture, where MISR refers to a multiple input signature register, and SRSG refers to a shift register sequence generator. The STUMPS architecture includes different channel scan paths (referred to as “channels” or “STUMPS channels”) that are each formed between a pseudo-random pattern generator (PRPG) (e.g., a linear feedback shift register (LFSR)) and the MISR, which is a state machine. Generally in a test (in a scan mode), an LBIST controller loads the multiple channel scan paths (STUMPS channels) with respective test patterns, and the IC is operated for one or more clock cycles. That is, the STUMPS channels apply the pseudo-random test data to the system logic or the macros from the PRPG. The operation changes the states at nodes of the circuit, and the state changes affect what is stored in one or more scan channel registers in the MISR. When the IC is returned to scan mode, the data in the MISR is shifted out and evaluated by comparing the obtained data with expected data.